Of an alloy to a support



United States Patent 3,172,829 METHOD OF APPLYENG A LAYER CQNSIS'HNG OF AN ALLOY TO A UPPRT Martinus Antonius Maria Baldrer and Banks Visser, both of Eindhoven, Netherlands, assignors to North American Philips Company, Inc., New York, N.Y., a corporatinn of Delaware No Drawing. Filed Jan. 22, 1962, Ser. No. 167,937 Claims priority, application Netherlands, Jan. 24, 1961, 260,428 5 Claims. (Ci. 204-35) The invention relates to a method of applying a layer consisting of an alloy to a support which may consist of metal.

In particular in the manufacture of metal contacts used in semi-conductor devices, such as transistors and crystal diodes, it may be required for these contacts to be provided with a layer consisting of an alloy, the composition of which must lie within close tolerances.

In certain cases, it is possible to produce a layer of such an alloy on the support by electro-deposition in a single operation by using a bath containing compounds of all the constituents of the alloy.

In order to obtain layers having a composition complying with precise prescriptions, in this method a number of factors, such as the composition and the temperature of the bath and the voltage and current density of the current have to be controlled within narrow limits.

It is also known to produce such layers by successive electro-deposition of the constituents of the alloy in the form of partial layers and then melting together. In this case each partial layer has to be deposited under accurately adjusted conditions.

It is an object of the invention to obviate these dis advantages.

According to the invention, the layer is produced by first applying at least one layer of the constituent of the alloy having the highest melting point, and then heat ing it in the presence of the other constituent or constituents at a temperature below the said melting point for so long a period of time that a solid solution of the other constituent or constituents is formed in this layer.

Preferably, at least one other constituent is applied in the form of a layer, the quantity applied exceeding that required for the formation of the alloy, after which the heating and formation of the solid solution takes place, the remaining material of the second layer being removed by dissolving it, preferably by etching.

Preferably, the heating process is continued for so long a period of time that the solid solution is in equilibrium with the excess of the other constituent.

The invention utilizes the fact that, apart from the properties of the constituents, the composition of the solid solution only depends upon the temperature and the duration of heating, the latter factor even being omitted when heating is at least continued for so long a period of time that equilibrium is attained.

The invention is particularly suitable for use in the manufacture of supports which are coated with a layer consisting of a gold-antimony alloy and which may be used for the formation of ohmic contacts on a semiconductor body consisting of germanium of the n-type.

Although in principle heating may be carried out at all temperatures underneath the melting point of gold, preferably the heating process is carried out at temperatures below 360 C. in order to prevent the formation of a molten gold-antimony alloy.

The invention will now be described more fully with reference to an example.

A plurality of supports consisting of the iron-nickel- "ice cobalt alloy known under the name of fernico, which supports have a total surface area of 1500 cm. are etched in concentrated hydrochloric acid for some minutes and then provided with a layer of nickel, which is not an essential feature of the invention but serves to improve the adherence of the subsequent layers. To this end, the supports are arranged in a drum in a bath containing per litre:

NiSO .6H O 200 NiCl 6H O 20 H BO 25 The treatment is carried out at 25 C. for half an hour with a current strength of 6 a.

Subsequently, a layer of gold is produced in a bath containing per litre:

Grams KAu(CN) 10 KCN 7 K CO .2H 0 30 This treatment is carried out at 70 C. for two hours with a current of 3 a.

Subsequently, a layer of antimony is produced in a bath containing per litre:

Grams K-Na tartrate.4H O 50 KOH 5 K-SbO tartrate. /2I-I O 5.5 K CO 2H O 10 This treatment is carried out at 25 C. for a quarter of an hour with a current of 5 a.

For the formation of a layer consisting of a solid solution of gold containing approximately 0.2 art-percent of antimony, the supports are subsequently heated in an inert atmosphere to 300 C. for half an hour, equilibrium then being substantially reached. As an alternative for the formation of a layer consisting of a solid solution of gold containing approximately 0.3 art-percent of antimony, the heat treatment is carried out at 330 C. during the same time. In both cases an inert atmosphere consisting of a gas mixture of VOL-percent of nitrogen and 10 VOL-percent of hydrogen at atmospheric pressure is used.

Finally, the excess of antimony is removed by Washing in concentrated sulphuric acid at 250 C. for three hours.

The supports may then be polished, for example by rote-finishing in water for half an hour, in order to remove any unevenness from the surface.

An n-type germanium body may then be attached to such a support by pressing the body against the support with a pressure of about 200 grams per square centimeter, for instance with a suitable weight, and heating the support and the body at a temperature of 400 C. for two minutes in a hydrogen atmospehre of atmospheric pressure.

Although by Way of example the manufacture of a layer consisting of gold-antimony alloy on a support is described, other suitable alloy-layers may be applied in a like manner. F.i. another suitable support consisting of molybdenum and covered with a layer consisting of gold-arsenic alloy may be prepared and a germanium or silicon body may be attached to it. So the gold layer may be applied in the manner as described above and the gold layer may be covered with an arsenic layer, for instance, evaporation in a manner known as such. Heat treatment may then be carried out at a temperature between 400 C. and 665 C. in a closed vessel containing for instance nitrogen at atmospheric pressure and saturated vapor of arsenic from a separate Grams 5" amount of solid arsenic in the vessel the vessel being heated totally at said temperature during a quarter of an hour to one hour. When using a. temperature of 610 C. a gold layer containing approximately 0.2 at.- percent of arsenic is formed by diffusion of the arsenic, the surplus of arsenic being subsequently dissolved for instance in concentrated nitric acid. Final polishing treatment and attaching a germanium wafer to it may be carried out in the manner as described above.

What is claimed is:

1. In the manufacture of a semiconductor device, a method of forming on an electrically-conductive substrate an alloy layer containing at least a first constituent having a higher melting point in major amounts and a second constituent having a lower melting point in minor amounts, said alloy layer containing the first and second constituents in certain desired proportions, comprising the steps of providing on the substrate a first layer of the said major constituent having the higher melting point, providing on the first layer a second layer of said minor constituent in an amount in excess of that required for forming the alloy of desired proportions with the first layer, heating the said layers at a temperature below the said higher melting point and at which the second layer diffuses into the first layer to form a solid solution therewith and without forming a molten phase, continuing the heating for a time at which sufiicient of the minor constituent is dissolved in the major constituent to form the alloy of desired proportions, and thereafter removing the excess undissolved material of the second layer leaving the desired alloy on the substrate, and thereafter securin the substrate to a semiconductive body with the desired alloy in contact with a surface of the semiconductive body.

2. A method as set forth in claim 1 wherein the excess material of the second layer is removed by etching.

3. In the manufacture of a semiconductor device, a method of forming on an electrically-conductive substrate an alloy layer containing at least a first constituent having a higher melting point in major amounts and a second constituent having a lower melting point in minor amounts, said alloy layer containing the first and second constituents in certain desired proportions with the minor constituent present in very small amounts, comprising the steps of providing on the substrate a first layer of the said major constituent having the higher melting point, providing on the first layer a second layer of said minor constituent in an amount in excess of that required for forming the alloy of desired proportions with the first layer, heating the said layers at a temperature below the said higher melting point and at which the second layer diffuses into the first layer to form a solid solution therewith and Without forming a molten phase, continuing the heating for a time at which sulficient of the minor constituent is dissolved in the major constituent to saturate the latter at the heating temperature and establish equilibrium with an excess of the minor constituent and at which the alloy of desired proportions is formed, and thereafter removing the excess undissolved material of the second layer leaving the desired alloy on the substrate, and thereafter securing the substrate to a semiconductive body with the desired alloy in contact with a surface of the semiconductive body.

4. A method as set forth in claim 3 wherein the major constituent is gold, and the minor constituent is antimony.

5. In the manufacture of a semiconductor device, a method of forming on a metal substrate an alloy layer containing at least a major amount of gold and a relatively minor amount of antimony in certain desired proportions, comprising the steps of providing on the substrate a first layer of the gold, providing on the gold layer a second layer of antimony in an amount in excess of that required for forming the alloy of desired proportions, heating the said layers at a temperature below 360 C. and at which the second layer diffuses into the first layer to form a solid solution therewith without forming a molten phase, continuing the heating for a time at which sulficient of the antimony is dissolved in the gold to form the alloy of desired proportions, and thereafter removing the excess undissolved antimony leaving the desired alloy on the substrate, and thereafter securing the substrate to a semiconductive body with the desired alloy in contact with a surface of the semiconductive body.

References tilted in the file of this patent UNITED STATES PATENTS 2,805,192 Brenner Sept. 3, 1957 2,814,589 Waltz Nov. 26, 1957 2,854,737 Gray Oct. 7, 1958 3,032,695 Zeilasek May 1, 1962 3,050,667 Emeis Aug. 2, 1962 3,075,892 John et al Jan. 29, 1963 FOREIGN PATENTS 1,190,078 France Mar. 31, 1959 844,266 Great Britain Aug. 10, 1960 

1. IN THE MANUFACTURE OF A SEMICONDUCTOR DEVICE, A METHOD OF FORMING ON AN ELECTRICALLY-CONDUCTIVE SUBSTRATE AN ALLOY LAYER CONTAINING AT LEAST A FIRST CONSTITUENT HAVING A HIGHER MELTING POINT IN MAJOR AMOUNTS AND A SECOND CONSTITUENT HAVING A LOWER MELTIN POINT IN MINOR AMOUNTS, SAID ALLOY LAYER CONTAINING THE FIRST AND SECOND CONSTITUENTS IN CERTAIN DESIRED PROPORTIONS, COMPRISING THE STEPS OF PROVIDING ON THE SUBSTRATE A FIRST LAYER OF THE SAID MAJOR CONSTITUENT HAVING THE HIGHER MELTING POINT, PROVIDING ON THE FIRST LAYER A SECOND LAYER OF SAID MINOR CONSTITUENT IN AN AMOUNT IN EXCESS OF THAT REQUIRED FOR FORMING THE ALLOY OF DESIRED PROPORTIONS WITH THE FIRST LAYER, HEATING THE SAID LAYERS AT A TEMPERATURE BELOW THE SAID HIGHER MELTING POINT AND AT WHICH THE SECOND LAYER DIFFUSES INTO THE FIRST LAYER TO FORM A SOLID SOLUTION THEREWITH AND WITHOUT FORMING A MOLTEN PHASE, CONTINUING THE HEATING FOR A TIME AT WHICH SUFFICIENT OF THE MINOR CONSTITUENT IS DISSOLVED IN THE MAJOR CONSTITUENT TO FORM THE ALLOY OF DESIRED PROPORTIONS, AND THEREAFTER REMOVING THE EXCESS UNDISSOLVED MATERIAL OF THE SECOND LAYER LEAVING THE DESIRED ALLOY ON THE SUBSTRATE, AND THEREAFTER SECURING THE SUBSTRATE TO A SEMICONDUCTIVE BODY WITH THE DESIRED ALLOY IN CONTACT WITH A SURFACE OF THE SEMICONDUCTIVE BODY. 